The present invention is an improvement on a retarding mechanism for a grinding machine of a prior patent application (with a filing number: R.O.C. Application No. 87220682). The retarding mechanism for the grinding machine of the prior patent application includes a body, a plane plate, a grinding member and a plurality of abrasive members. Wherein, the body is provided therein with a motor of which a driving axle combines with an output axle, the output axle extends out of the body and can be driven by the driving axle of the motor for rotation. The body encircling the output axle is fixedly provided with an annular plane plate. The grinding member is fixedly provided with a fixing seat on the rear surface thereof by means of screws, and with a grinding tool on the front surface thereof. The fixing seat is provided on the periphery thereof with a plurality of grooves which each has a through hole on the bottom thereof. The abrasive members are made of material with low friction coefficient (such as Teflon, plastic etc.) The abrasive members are bending strips each with a width to be exactly receivable in the grooves. One end of each abrasive member has a through hole. The mode of combination of the abrasive members with the fixing seat is: one end of each abrasive member is received in one of the grooves to have two corresponding through holes aligned with each other, then a screw is extended through the two holes, and a nut is locked on the screw to fix the abrasive member in the groove. When the grinding member is assembled on the output axle extending out of the body, the bending protruding portion of the abrasive member contacts and presses the plane plate appropriately. In the mean time, if the grinding member is driven for rotating, the abrasive member will be rotated therewith, and friction force will be induced between the abrasive member and the plane plate to slow down the rotation speed of the grinding member.
However, the bending protruding portion of the abrasive member is structurally elastic, when elasticity thereof is weakened, the abrasive member tends to deviate; and height of the protruding portion is unable to be controlled, so friction force between the abrasive member and the plane plate can not be large, and can not effectively slow down the rotation speed of the grinding member. In view of this, the present invention provides improvement on the existed defect in speed reducing of the prior retarding mechanism for a grinding machine.